1. Field of the Invention
This invention relates to downhole tools; particularly, though not exclusively, to an improved casing centraliser; and more particularly, though not exclusively, to a casing centraliser for facilitating cementing of casing in a well.
2. Description of Related Art
After a well section has been drilled, it is necessary to secure a borehole of the well section by lining it with a pipe known as oilfield xe2x80x9ccasingxe2x80x9d or xe2x80x9clinerxe2x80x9dxe2x80x94or generically xe2x80x9ctubularxe2x80x9d.
Having installed the casing or liner within the borehole, it is necessary to make a seal in an annular space formed between the borehole and an outer surface of the pipe. This seal provides both a strengthening role forming a composite structure of the steel pipe and the seal itself, as well as a barrier to the possible flow of fluid contained in one geological strata to another to the surface at a well head. Such a seal is usually achieved by displacing the drilling fluid in which the pipe was run, and which is thus contained in the annular space, with a cement slurry which subsequently hardens forming an impermeable barrier or sheath.
The success of cementation operations is largely determined by the displacement efficiency of the cement slurry as it displaces drilling fluid from the annulus.
This displacement efficiency is maximised by a number of factors, these include xe2x80x9ccentralisationxe2x80x9d of the pipe (i.e. aligning the axis of rotationxe2x80x94longitudinal axisxe2x80x94of the pipe with a centre of the borehole). This keeps the pipe off the borehole wall as much as possible. In addition reciprocation of the pipe where practicable; and the creation of a degree of turbulent flow in the annulus while pumping the slurry.
From the foregoing it is clear that pipe movement forms a critical role in securing a borehole after drilling operations, both in terms of getting the pipe to the bottom of the well, where drag forces are critical factors and in maximising the displacement efficiency of the cement slurry, in which rotational forces and centralisation are critical factors.
Boreholes are generally becoming deeper and more tortuous than ever before as Operators strive to access near field potential hydrocarbon reserves (i.e. marginal reserves close to existing infrastructure) in an effort to extend the life of their facilities. There is, therefore, a need in the industry to reduce the dynamic forces, drag and torque, required to secure the casing and liner in these boreholes thereby creating a competitive advantage over conventional equipment.
Known casing/liner centralisation and cementing accessories are made of metals such as steel, zinc and aluminium.
U.S. Pat. No. 5,095,981 (MIKOLAJCZYK) discloses a casing centralizer comprising a circumferentially continuous tubular metal body adapted to fit closely about a joint of casing, and a plurality of solid metal blades fixed to the body and extending parallel to the axis of the body along the outer diameter of the body in generally equally spaced apart relation, each blade having opposite ends which are tapered outwardly toward one another and a relatively wide outer surface for one another and a relatively wide outer surface for bearing against the well bore or an outer casing in which the casing is disposed, including screws extending threadedly through holes in at least certain of the blades and the body for gripping the casing so as to hold the centralizer in place.
WO 91/05093 (WEATHERFORD) discloses apparatus for use with a tubular member, which apparatus comprises: a generally cylindrical hollow body having an inner surface of substantially uniform diameter, an outer surface, a first end and a second end, and disposed on a tubular member a plurality of ribs extending from and spaced apart on said body, characterised in that the distance between at least one adjacent pair of ribs and/or the thickness of the generally cylindrical hollow body is not uniform throughout the length of the apparatus.
EP 0 671 546 A1 (DOWNHOLE PRODUCTS) discloses a casing centraliser comprising an annular body, a substantially cylindrical bore extending longitudinally through said body, and a peripheral array of a plurality of longitudinally extending blades circumferentially distributed around said body to define a flow path between each circumferentially adjacent pair of said blades, each said flow path providing a fluid flow path between longitudinally opposite ends of said centraliser, each said blade having a radial outer edge providing a well bore-contacting surface, and said cylindrical bore through said body being a clearance fit around tubular casing intended to be centralised by said casing centraliser, the centraliser being manufactured from a material which comprises zinc and preferably a zinc alloy.
The content of the abovementioned prior art citations is incorporated herein by reference.
It is an object of one or more aspects of the present invention to obviate or mitigate problems in the prior art.
It is a further object of one or more aspects of the present invention to seek to meet the aforementioned industry need.
According to a first aspect of the present invention there is provided a casing centraliser at least a portion of at least one surface of which is selected from a material comprising a plastics material or a ceramic material, cermet or submicron grained cemented carbide.
Each material has a number of advantages over the other.
Advantageously the plastics material may be a polymer of carbon monoxide and alpha-olefins, such as ethylene.
Advantageously the material may be an aliphatic polyketone made prom co-polymerisation of ethylene and carbon monoxidexe2x80x94optionally with propylene.
Advantageously the material may be CARILON (Trade Mark) available from Shell Chemicals. CARILON (Trade Mark) is a class of semi-crystalline thermoplastic materials with an alternating olefinxe2x80x94carbon monoxide structure.
Alternatively the plastics material may be a nylon resin.
Advantageously the plastics material may be an ionomer modified nylon 66 resin.
Advantageously the plastics material may be ZYTEL (Trade Mark) available from Du Pont. ZYTEL (Trade Mark) is a class of nylon resins which, includes unmodified nylon homopolymers (e.g. PA 66 and PA612) and copolymers (e.g. PA 66/6 and PA 6T/MPMDT, etc.) plus modified grades produced by the addition o heat stabilizers, lubricants, ultraviolet screens, nucleating agents, tougheners, reinforcements, etc. The majority of resins have molecular weights suited for injection moulding and some are used in extrusion.
Alternatively the plastics material is VESCONITE (Trade Mark) available from Vesco Plastics Australia Pty Ltd.
Alternatively the material may be polytetrafluoroeth(yl)ene (PTFE).
In such case the material may be TEFLON.
The ceramic material may be, for example, zirconia, titania and/or alumina. The ceramic material may be toughened by addition of a further material, for example zircoria with the addition of alumina.
The casing cencraliser may comprise a tubular body.
The tubular body may have a bore extending longitudinally therethrough.
The body may provide an outermost surface and an innermost surface.
The outermost surface may provide a plurality of raised portions.
The raised portions may be in the form of longitudinally extending blades or ribs or may alternatively be in the form of an array of nipples.
Adjacent raised portions may define a flow path therebetween such that fluid flow paths are defined between first and second ends of the tubular body.
Where the raised portions comprise longitudinal blades, such blades may be formed substantially parallel to an axis of the tubular body.
Alternatively, the blades may be formed in a longitudinal spiral/helical path on the tubular body.
Advantageously adjacent blades may at least partly longitudinally overlap on the tubular body.
Preferably adjacent blades may be located such that one end of a blade at one end of the tubular body is at substantially the same longitudinal position as an end of an adjacent blade at another end of the tubular body.
More preferably, the blades may have an upper spiral section, a middle substantially straight portion and a lower tapered portion.
Each raised portion may provide a wellbore contacting surface.
The bore through the body may be a clearance fit around a tubular casing intended to be centralised by the centraliser.
In one embodiment the outermost and/or innermost surfaces of the centraliser may be selected from a plastics material or a ceramic material, cermet or submicron grained cemented carbide, and advantageously comprise CARILON
In such an embodiment the outermost and/or innermost surfaces may comprise a coating formed on an inner tubular body.
The inner tubular body may be made of a metallic material such as steel, zinc, zinc alloy, or preferably from aluminium or aluminium alloy.
In a further, preferred embodiment the body may be made from a material selected from a plastic material or a ceramic material, and advantageously may be CARILON.
The casing centraliser according to the first aspect of the present invention may be formed from a casting process.
Alternatively and advantageously the casing centraliser according to the first aspect of the present invention may be formed from an injection moulding process.
Advantageously the casing centraliser may be formed with the innermost surface providing at least one and preferably a plurality of spaced apart longitudinally extending tapered recesses. The recess(es) may taper from an upper end towards a lower end of the centraliser.
According to a second aspect of the present invention there is provided a wellbore casing apparatus including a well casing and at least one casing centraliser located thereupon, wherein at least a portion of at least one surface of the centraliser is selected from a material comprising a plastics material or a ceramic material, cermet or submicron grained cemented carbide.
The well casing is preferably of a hollow tubular form.
Further the at least one centraliser may comprise a tubular body.
The at least one centraliser may be located so as to surround the casing.
The at least one centraliser may be located relative to the casing by means of a collar.
The at least one centraliser may be located relative to the casing and may be rotatable relative to the casing along a longitudinal axis thereof.
According to a third aspect of the present invention there is provided a method of cementing a well casing into a well bore, the method comprising the steps of:
providing a well casing;
providing at least one casing centraliser, the/each centraliser comprising at least a portion of at least one surface of which is selected from a material comprising a plastics material or a ceramic material, cermet or submicron grained cemented carbide;
locating the at least one centraliser on the casing a desired position so as to provide a casing apparatus;
placing the casing apparatus with the borehole;
pumping cement into an annular space between an exterior of the casing and the wellbore.
According to a fourth aspect of the present invention there is provided a downhole device/apparatus/tool at least a portion of at least one surface of which is selected from a material comprising a plastics material or a ceramic material, cermet or submicron grained cemented carbide.
Each material provides a number of advantages over the others.
The downhole device/apparatus/tool may be, for example, a casing, a casing centraliser, a protector, a stabiliser, a liner/a glider, and/or a turbulating clamp, an anti-casing war device such as a non-rotating drill pipe protector or sacrificial wear bushing, a logging/wireline conveyed tool/tool string, and/or a control line clamp for the purpose of actuating downhole safety devices, gauges and/or pumps.
Advantageously the material may be a thermoplastic polymer.
Advantageously the material may be polymer of carbon monoxide and alpha-olefins, such as ethylene.
Advantageously the material may be an aliphatic polyketone made from co-polymerisation of echylene and carbon monoxidexe2x80x94optionally with propylene.
Advantageously the material may be CARILON (Trade Mark) available from Shell Chemicals. CARILON (Trade Mark) is a class of semi-crystalline thermoplastic materials with an alternating olefinxe2x80x94carbon monoxide structure.
Alternatively the material may be polytetrafluoroeth(yl)ene) (PTFE).
In such case the material may be TEFLON.
The ceramic material may be, for example, zirconia, titania and/or alumina. The ceramic material may be toughened by addition of a further material, for example zirconia with the addition of alumina.
The device may comprise a main body.
The main body may comprise or be at least partially coated with the material.
According to a fifth aspect of the present invention there is provided a casing centraliser comprising a tubular body having an outermost surface carrying a plurality of raised nipple portions.
The plurality of raised nipple portions may comprise an array of portions, adjacent portions being substantially equally spaced around the outermost surface.
According to a sixth aspect of the present invention there is provided a casing centraliser comprising an outermost surface, the outermost surface providing a plurality of raised portions, the raised portions are in the form of longitudinally extending blades or ribs, the blades or ribs are formed in a longitudinal spiral/helical path on a tubular body wherein adjacent blades are located such that the top of a blade at a first end of the tubular body is at the same longitudinal position as the bottom of an adjacent blade at a second end of the tubular body.
Preferably the blades or fins have an upper spiral section, a middle substantially straight portion and a lower tapered portion.
According to a seventh aspect of the present invention there is provided a casing centraliser at least a portion of at least one surface of which is coloured wherein the colour identifies an outer and/or inner diameter of the casing centraliser.
According to an eight aspect of the present invention there is provided a colour coded set of casing centralisers comprising a plurality of casing centraliser, each casing centraliser has at least a portion of at least one surface coloured wherein the colour identifies an outer and/or inner diameter of the casing centraliser.
According to a ninth aspect of the present invention there is provided a casing centraliser composing a radioactive element, wherein the radioactive element is traceable to reveal the position of the casing centraliser when located in a wellbore.
One or more of the nipple portions may be substantially parallelogram or diamond shaped.
Adjacent raised nipple portions may define a flow path therebetween such that a fluid (cement) flow pth/paths are defined between first and second ends of the tubular body.